Linked projects put the filters on the opposite side to what you're suggesting. Can you elaborate more on why do you think the filters should act on the air coming into the fan? Is it to increase heat dissipation of the motor?
putting it on the intake keeps the motor cleaner (which will help with motor life), you can vacuum the filter without disassembly, and the air flow will tend to help the filter stay on, instead of pushing it away.
